FILE - In this Dec. 22, 2013, file photo, Kansas City Chiefs tackle Donald Stephenson (79) waits for a play to start during the second half of an NFL football game against the Indianapolis Colts at Arrowhead Stadium in Kansas City, Mo. (AP Photo/Ed Zurga, File)

KANSAS CITY, Mo. (AP) — Chiefs offensive tackle Donald Stephenson was suspended by the NFL for the first four games of the regular season Friday for violating the league’s performance-enhancing substance policy, a massive blow to an already unsteady offensive line.

Stephenson remains eligible to participate in all preseason practices and games, including Saturday night’s contest against Minnesota. He will miss games against Tennessee, Denver, Miami and New England and be eligible to return to the active roster Sept. 30.

The substance was not disclosed. The Chiefs said in a three-sentence statement that they were informed of the positive test on Friday and expressed disappointment in losing Stephenson, but declined further comment.

Stephenson said in a statement issued through the NFL Players’ Association that he took a medication that requires a therapeutic-use exemption and failed to properly investigate it.

“The rules are strict, and without a TUE, the consequence is a four-game suspension,” Stephenson said in the statement. “It is not a mistake I will ever make again. I will train extremely hard during my time away from the team and I will be ready to contribute to my team’s effort to win a Super Bowl as soon as I return.”

Stephenson was a fill-in starter last season but was expected to anchor the right side this year, taking over for former No. 1 overall draft pick Eric Fisher as he moved back to left tackle.

With perilously little depth, Stephenson’s lost could result in plenty of shuffling.

Jeff Allen is expected to move from left guard to right tackle, filling in for Stephenson but creating a new hole. Ricky Henry and Jeff Linkenbach, who were fighting for a backup job, are now in a race to replace at Allen at starting left guard for the first four games of the season.

“We’re rotating people around and we’ll keep doing that,” Chiefs coach Andy Reid said. “When we’re satisfied with who the five best are we’ll roll from there. I don’t really care about positions right now. I just care about getting the five best out there.”

The Chiefs have tried several permutations through their first two preseason games, and none of them has engendered a great deal of confidence. If they haven’t been hit with false start and holding penalties, they’ve struggled to open holes and contain the pass rush.

“We don’t make any excuses for them,” offensive coordinator Doug Pederson said. “Guys just have to focus in on detail. They get in the heat of the battle and sometimes they get a little fatigued and into the game, but they still have to concentrate and understand how we’re snapping the ball, when we’re snapping the ball. We need to eliminate those types of penalties, the holding penalties and obviously the sacks and turnovers.”

The trickle-down of Stephenson’s suspension could also impact the number of offensive linemen the Chiefs keep when they go through roster cuts. Teams must trim from 90 players to 75 by Tuesday afternoon, and final cuts to the 53-man roster limit are due Sept. 30.

The Chiefs were already without their top wide receiver, Dwayne Bowe, for the season opener after he was suspended by the league for an incident involving marijuana last November.

They’ve also been dealing with a rash of injuries. Inside linebacker Joe Mays sustained a wrist injury that will require surgery and is likely to keep him out for the first few weeks of the regular season, and running back Jamaal Charles, safety Eric Berry and wide receiver Junior Hemingway have all been dealing with nagging injuries during training camp.